Patent Document 1 discloses a hydraulic brake system including (a) a master cylinder, (b) a power hydraulic-pressure generating device including a pump device and an accumulator, (c) a plurality of brake cylinders and (d) a common passage to which these elements are connected, wherein an output hydraulic-pressure control valve is disposed between the power hydraulic-pressure generating device and the common passage. When the hydraulic brake system is in a normal state, hydraulic pressure outputted from the power hydraulic-pressure generating device is controlled by control of the output hydraulic-pressure control valve such that the controlled hydraulic pressure is supplied to a plurality of brake cylinders via a common passage. When an electric line of the hydraulic brake system is in a failure state, the power hydraulic-pressure generating device is isolated from the common passage, and the hydraulic pressure in the master cylinder is supplied to the plurality of brake cylinders via the common passage.
Patent Document 2 discloses a hydraulic brake system in which a power hydraulic-pressure generating device is connected, via a valve mechanism 13 and shuttle valves 17, 18, to fluid passages connecting a master cylinder and brake cylinders. The shuttle valves 17, 18 are configured to select a higher one of the hydraulic pressure in the valve mechanism 13 and the hydraulic pressure in the master cylinder, and the selected one is supplied to the brake cylinders.
Patent Document 3 discloses a hydraulic brake system in which each of individual control valves is disposed in midway of a corresponding one of fluid passages connecting a power hydraulic-pressure generating device and brake cylinders. A master cylinder is connected to portions of the respective fluid passages each of which is located on a downstream side of the corresponding individual control valve. When the hydraulic brake system is in a normal state, the hydraulic pressures in the brake cylinders are controlled by utilizing the hydraulic pressure in the power hydraulic-pressure generating device with controls of the respective individual control valves while the brake cylinders are being isolated from the master cylinder. When an electric line of the hydraulic brake system is in a failure state, the hydraulic pressure in the master cylinder is supplied to the brake cylinders.
Patent Document 4 discloses a hydraulic brake system in which, after a vacuum booster has reached its boosting limit, the hydraulic pressure outputted from a pump device is controlled, and the controlled hydraulic pressure is supplied to a pressure chamber that is located on a rear side of a pressurizing piston of a master cylinder. Owing to this arrangement, the hydraulic pressures in the respective brake cylinders can be increased after the vacuum booster has reached its boosting limit, such that a ratio of the hydraulic pressure in the brake cylinder to a brake operating force is not changed between before and after the vacuum booster reaches its boosting limit. In this hydraulic brake system, a relief valve is disposed between the pump device and a main passage connecting the master cylinder and the brake cylinders, such that a pressure discharged from the pump device is supplied to the main passage via the relief valve when the pressure discharged from the pump device becomes excessively high.